1994 Libby MEP 802A 5kW Generator High Blowby looking for advice

[dskupi01]

Onan DN2M Diesel, 2 cylinder/4 stroke, 11.0hp @1800 RPM, 24VDC start, liquid-cooled.

Got unit a few months back from Govplanet. 80 hours. Unit has high blowby, but not so high it pushes out the dipstick.

I've tested the unit, and it's 100% functional, with the exception of the blowby. Starts instantly, and doesn't bog down until about 120%+ load. I have run the unit a few hours (low load) and short periods at higher loads. No long runs at 80-100% load.

Here's the question. I think with some feedback from others w/ experience on this specific engine, I can make a determination on the next steps.

I am guessing one of two problems:
1. Broken, collapsed, or sludge stuck fire ring.
2. Rust in a cylinder because it was left un-run for a long period (one open cylinder). This then caused surface rust, and the cross hatch on cylinder bore to rusted/degraded (then fire ring wear). I don't think it was an issue with significant water down the exhaust, as there are no other signs of this. Exhaust flap was also in place.

Anyone know if this engine has a tendency to stick/collapse/fracture fire rings?
Options:
1. Run the engines as is? It makes power, but the high blow-by would likely case minor crankcase leaks. Engine starts instantly, and I'd likely run only about 100 hours per year.
2. Take it apart. Re-hone and replace rings.
3. Take a risk and run at full load for a few hours to see if the rings seal up? Risk there is doing more damage, which would require OS pistons vs a hone. If fire-ring is in two pieces already, it would likely lunch the engine.
4. Know if there are other issues causing high blowby? Manual alluded to a passage between the intake manifold to crankcase to maintain negative crankcase pressure.

Thanks for suggestions

David S. Detroit Mi.

 

[DieselAddict]

I would run it with progressively higher loads for a full day and see if it gets better. If after 3-4 hrs at 75% or more load nothing changes you have to decide to live with it or go into the engine to resolve it.

Have you run it long enough to see its oil consumption rate? Does it look like it's stacking oil up on top of the head?

 

[Triple Jim]

I don't mean to insult you, but what is the symptom of the high blowby? This is a 2-cylinder engine with both pistons moving up and down together, so there will be a lot of crankcase pressure pulsing, compared to a 4-cylinder with very little. I'm asking because the engine starts easily and its performance is so good (capable of 120% power).

 

[Guyfang]

Tripple Jim,

The Onan engine, both 2 and 4 cylinder, are supposed to have a vacuum in the crankcase. There is simple instructions on how to make a water Manometer in the -24 manual. If there is ANY positive pressure on the crankcase, there is some sort of problem. They ca and do sometimes shoot the oil dipstick out of its holder in extreme cases. At least twice I have pulled the dipstick while running, and got a shot of hot oil on my chest and face. Not nice.

 

[Eliteweapons]

A quick question. What pre-start procedure did you use on the engine that sat open for so long? If you just fired it up then you may have broken the rings that were probably rusted to the cylinder wall and scored the walls up pretty good. Is the breather system clean and working correctly?

 

[Triple Jim]

At least twice I have pulled the dipstick while running, and got a shot of hot oil on my chest and face. Not nice.

I would expect a 2-cylinder to do that even if everything is working perfectly. Even with the crankcase averaging a vacuum, there's going to be a large amount of pulsing of pressure from the pistons going up and down together.

 

[Guyfang]

For some reason the picture of the manometer didnt come through. But here it is, the test and what it should read.

3-5. CRANKCASE VACUUM,3-5.1. General. The value depends to some extent on the type and size of air cleaner installed on the engine.Regardless of type air cleaner used, vacuum with a clean air cleaner must not be less than a minimum of 0.79 in. (20mm) water gage (WG). The vacuum is measured with a manometer at the lubricating oil dipstick hole with the enginerunning. In engines in good condition vacuum increases slightly with engine speed but not proportionally. A fluctuatingvacuum may indicate faulty oil seals, valves, or piston blow-by troubles. Crankcase pressure can cause serious oil leaksand often occurs in engines which need overhauling.3-5.2. Measure Vacuuma. Remove lubricating oil dipstick.b. If water manometer is available, connect one end of a 0.374 in. (9.5 mm) OD plastic tube to a water manometer.Insert other end of tube into dipstick hole, refer to FIGURE 3-1.NOTEAverage vacuum should be 1.37 in. (34.8 mm) WG. Minimum allowed is 0.79 in. (20 mm) WG.WarningThe noise level when operating could cause hearing damage. Ear protection must be worn.

c. Start engine and record reading on manometer.d. Stop engine, disconnect manometer and install oil dipstick.e. If water manometer is not available, place a piece of thick paper over the oil fill opening. If crankcase vacuumretains paper, vacuum is good.FIGURE 3-1. Locally Manufactured Water Manometer

 

[dskupi01]

Thanks for the feedback. Gov Planet started it prior to auction, so unfortunately I couldn't pre-lube.

It definitely, has positive crankcase pressure. There's also a paper test in the manual, I think it would certainly fail. "If water manometer is not available, place a piece of thick paper over the oil fill opening. If crankcase vacuum retains paper, vacuum is good." I also compared the video of other 802s sold (shown by gov planet), where they show no crankcase pressure. In comparison, my unit is bad. But, I knew this going in.

I am hoping a stuck ring, which I can unstick (wishful thinking). At worse, some honing and new rings, or combine with another auctioned unit to get a whole unit.

For before on crankcase pressure, search govplanet for item number 861690. One of the photos shows the blowby. A video shows the before. I will change oil, and run it 24 hours and show the after in a few days.

I see no signs of oil burn or passing oil (blue smoke or wet stacking/oil out exhaust).

 

[dskupi01]

Does anyone know if there's a passage in the intake manifold to crankcase to pull the vacuum? I would check this also to make sure not sludge plugged (unlikely).

 

[Guyfang]

Make or procure a water manometer. Perform the test IAW the TM. Then pull the injectors, spray in for WD/40, or wonder oil or what ever. Mabe a couple ounces, or more, in each cylinder. Let it set a day or two. Use the S-10 to turn the engine over, for a few seconds, to remove any extra fluid. Warning. If there is any fluids in the cylinders, there will be some significant spray out of the injector ports.

Then replace the injectors. Run for an hour. Then try the manometer again. Compare the readings. There is NO SENSE in trying to losen up the rings, without having a baseline reading, and a post "ring loosing" reading. The paper test is naturally a field expedient. Ball park figure only. The only time I would use it is if I am standing in a field in the middle of BF Afghanistan.

What does the below listed sentence mean?

For before on crankcase pressure, search item number 861690.

 

[dskupi01]

Sorry. Should have read. search govplanet for item number 861690. One of the photos (a video) shows the blowby.

 

[Daybreak]

Howdy,

GovPlanet 1994 Libby MEP-802A on a little trailer

in the picture set, #31 shows Engine - Blow by @ idle (subjective observation) Significant

I would be surprised that after running 2 hours there would be any oil left in the unit.

The entire insides are coated with oil and ____? fuel maybe...

 

[DieselAddict]

Ouch. Yea, that looks like it's going to be a tear-down. It won't hurt to give the soaking that Guy suggested. After seeing how much pressure you have in the crankcase I have doubts it will come back without a rebuild.

 

[Guyfang]

Having seen much worse, (yes, much worse, and still running) I would still try and soak the pistons, because its a cheap way to make sure to test the cylinders, if you cant use, dont have a compression tester.

But you know, I didnt see any missing parts. A few screws, yeah. It got old style switches, but if they work, why screw with them. All in all, not a bad gen set, if you could get it cheap. And I think someone in the forum might have a new engine, if you didnt want to fool with a rebuild, if it needs it.

Oh, yeah. The trailer. That baby looks like home built. I would bet a case of beer, its not military issue.

 

[fuzzytoaster]

Oh, yeah. The trailer. That baby looks like home built. I would bet a case of beer, its not military issue.

I'll take you up on that bet. It's an M762 1/4 ton flatbed for a M151 MUTT. Heck, if the trailer is in decent condition sell the trailer and you end up with a free generator!

http://g503.com/forums/viewtopic.php?f=28&t=207468

 

[dskupi01]

Changed oil on the unit. Changed both fuel filters. Added the 3amp slow blow fuse fix to the #8 quad output on the voltage regulator. Ran 2 hours at 50% load. Will up to load 75 % for four hours next. See video link for the unit running and vitals. 200f on coolant temp gauge. I am guessing reads high compared to real temp. Will test once I get some time.

When running, oil filler is closed, so keeping oil in no problem. The other video on govplanet shows a fuel leak, which was addressed with some new fuel hose & clamp force. This shouldn't be confused with the high ccp. They are unrelated.

Video of unit. I assume okay to link to YouTube?
https://youtu.be/vbzfTeZK1_o

 

[Triple Jim]

I would get a manometer on it and see what's really happening before I assumed anything. If I take off the oil filler cap on a single cylinder Briggs and Stratton engine, oil and vapor will come flying out and go all over the place because of the crankcase pumping, yet the engine is in perfect condition.

 

[Guyfang]

Where do I ship the beer?

Nuf said!